docs: def close_idle_connections(self, pool_id=None):
          """close idle connections to mongo"""
          if not hasattr(self, '_pools'):
              return
  
          if pool_id:
              if pool_id not in self._pools:
                  raise ProgrammingError("pool %r does not exist" % pool_id)
              else:
                  pool = self._pools[pool_id]
                  pool.close()
          else:
              for pool_id, pool in self._pools.items():
                  pool.close()